The present invention relates to helical conveyors, and more particularly, to self-stacking helical conveyors for use in continuous processing of materials, such as freezing or cooking food products, for example.
Endless conveyors for continuous processing of materials loaded and unloaded continuously to and from an endless conveyor belt must have a working length adequate to permit a required duration of time in a processing environment and, at the same time, be movable at sufficiently high conveying speeds for acceptable rates of processing production. To meet these requirements, and also to reduce the space requirements of the processing environment, helical conveyors have been developed in which a working belt length, representing a substantial portion of the overall conveyor belt length, is carried through a continuous succession of vertically oriented helical flights or tiers. In this manner, a long working length of the conveyor belt may be contained in a reasonably dimensioned processing enclosure, such as a freezer, while loading and unloading lengths of the conveyor belt may be located outside of the enclosure.
The prior art relating to helical conveyors is exemplified by several U.S. Pat. Nos. including No. 2,093,270--Glinka, No. 4,450,953--Le Cann et al., No. 4,982,833--Straight et al., and No. 5,105,934--Cawley.
Glinka represents an early development in helical conveyors from the standpoint of recognizing the advantages of helical conveyors for processing (i.e., drying or otherwise treating) materials by taking advantage of the reduced space requirements of such conveyors. Le Cann et al. may be characterized as an early attempt at a solution to the mechanical problems associated with driving an endless flexible belt through a helical path. Also, Le Cann et al. represents a self-stacking approach to helical conveyors by using upstanding plate-like supports on opposite side edges of the conveyor belt to support successive tiers or "spires" of the endless belt one on the other.
Straight et al. and Cawley are representative of more recent developments in that these latter prior art references address mechanical details associated with elevating a lower-most first flight or tier in an endless belt from a horizontal run to an inclined helical turn or tier on which successive vertical tiers are supported at least on the inboard edge of a helical conveyor. The earlier Straight et al. patent cites prior U.S. patents which advantageously disclose helical belt systems in which both inner and outer edges of the endless belt are self supporting. The text of the Straight et al. patent points out that while prior attempts at self-support for both edges of an endless helical belt were advantageous from the standpoint of minimizing space occupied by the working length of a helical belt, such belts suffered a disadvantage in that the belt tier supports presented an obstruction to circulation of a processing atmosphere, i.e., cooling air, about products supported on the belt. Cawley likewise discloses an endless helical belt for processing products in which only the inboard edge of the belt is self-supporting and the outboard edge is supported by a helical ramp extending throughout the length of the helical belt length.
Both the Straight et al. and Cawley patents disclose helical conveyor systems in which support for the bottom tier of a vertically oriented helical belt is supported by trolleys which travel on a circular track aligned under the inboard edge of the belt. Also, the disclosures of both patents employ a transitional track section to support the belt over a depressed ramp portion of the circular track at which the trolleys release and engage successive bottom tiers exiting or entering the helical belt stack.
Although the prior art relating to helical conveyors, therefore, has been developed to some degree, there has been and is need for improvement.